The present invention relates to an image processing apparatus, a printing apparatus and an image processing method, each of which is employed for outputting data representing a test chart to be used for an image quality correction processing.
In the printing apparatus, such as a printer, an MFP (Multi-Functional Peripheral), etc., in order to suppress the deterioration of an image quality of the printed image due to changes of printing characteristics caused by the degradation of the pans, the change of the parts, or another adverse factor, a patch image to be used for correcting the image quality of the printed image is printed in advance, so as to conduct the operation (calibration) in regard to the printing characteristics by measuring the image quality of the patch image printed.
For instance, Tokkai 2008-288968 (Japanese Patent Application Laid-Open Publication) sets forth such technology that the gamma characteristic (density gradation characteristic) is corrected so as to coincide the density represented by the image signal with the toner density of the image to be actually printed. Specifically, Tokkai 2008-288968 sets forth such the method that includes: printing the correction patch images including a plurality of gradation levels (such as 256 gradation levels, etc.); measuring brightness of each of the patch images so as to select sample points in regard to the plurality of gradation levels; arranging each of the sample points onto a brightness-gradation coordinate domain in the descending order or the ascending order of the gradation values; trying to detect an interval of an inflection point or an interval of a straight line from the intervals between the sample points; changing the interpolating method of the sample points corresponding to the detected results, so as to approximately acquire the consecutive gradation characteristic.
Further, since, sometimes, density unevenness would occur in the main-scanning direction of the printed image in the scanning-type printing apparatus, the operation for correcting the density unevenness in the main-scanning direction is also conducted. FIG. 9 shows a schematic diagram indicating an example of a conventional test chart 80 to be employed for measuring and correcting the density unevenness in the main-scanning direction.
In this case, since the density of the image is measured in the main-scanning direction, patch images 90, density of each of which is uniform (has a constant gradation value) over the printing range in the main-scanning direction. Further, in the configuration in which a plurality of image forming sections respectively corresponding to the primary colors of color Y (Yellow), color M (Magenta), color C (Cyan) and color K (Black), since, sometimes, the density unevenness of each of the primary colors in the main-scanning direction tends to differ from another one of the primary colors due to the differences between the parts employed in the image forming sections concerned, the patch images 90 are printed for every primary color. Still further, considering the gamma characteristic (density gradation characteristic) abovementioned, the patch images 90 corresponding to a plurality of gradation values are printed. For instance, eight patch images 90 are printed for every group of 32 gradation levels among the 256 gradation levels (input gradation levels of 0-255).
According to the abovementioned, in the test chart shown in FIG. 9, 32 patch images 90 ((4 colors of Y, M, C and K)×(8 patches)) are printed, so that the density unevenness of each of the patch images 90 in the main-scanning direction, which is printed on the test chart test chart 80, is measured, so as to calculate a correction value for correcting the density unevenness for every main-scanning position in regard to each of the colors of Y, M, C and K, based on the above-measured values. With respect to a correction value for a gradation level that has not been actually measured, the concerned correction value is found by conducting an interpolation arithmetic calculating operation, such as the linear interpolation processing, etc., from the measured correction values of the gradation levels.
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When the conventional test chart as abovementioned is employed, since the correction accuracy would be degraded in such a case that the number of patch images is too small, even if the linear interpolation processing is conducted, it is necessary to increase the number of patch images to some extent in order to secure the correction accuracy. However, the lager the number of patch images increases, the longer the time for measuring the density unevenness is required, resulting in an increase of consumptions of paper sheets and toner, and waste of time and materials.